Gibberellins are a class of plant growth regulators which are diterpenoid acids. Gibberellins are commercially produced by fermentation of a natural fungus, Gibberella fugikuroi. Gibberellins are marketed under various trade names and are commercially used on a variety of fruit orchards, vegetable crops, row crops, and ornamental crops. The predominantly used gibberellin is gibberellin acid (“GA3”).
Gibberellins have been formulated in numerous ways over the years in order to attempt to overcome their low solubility. For example, gibberellins have been formulated as solutions, soluble powders, wettable powders, tablets, and water-dispersible granules. The disadvantages of each category of the prior art formulations are discussed below.
Solution formulations of the prior art are disadvantageous in several respects. The formulations are less concentrated due to low solubility of gibberellins, have limited storage stability, and/or contain unacceptable amounts of volatile organic compounds (“VOCs”).
The low solubility of GA3, gibberellin4 (“GA4”), or gibberellin4/7 (“GA4/7”) in some solvents, such as propylene glycol, does not permit preparation of high concentration solution formulations. These low strength solution formulations require larger packaging, more storage space, and higher associated transportation, warehousing, and container disposal costs. Due to very low solubility and undesirable hydrolysis, it has been especially difficult to formulate GA3 in aqueous systems.
In order to overcome solubility issues, some formulations use solvents with amounts of VOCs that are not safe for the environment. For example, isopropyl alcohol and methyl alcohol offer severe disadvantages such as flammability and toxicity, which lead to restrictions in manufacturing, packaging, labeling, transportation, and warehousing of such solutions. Tetrahydrofurfuryl alcohol (“THFA”) is considered corrosive to the eye and skin.
One way to overcome the solubility issues with GA3, GA4, and GA4/7 is to prepare soluble powder formulations. These powder formulations dissolve readily when mixed with water and form true solutions. Once the solution is formed, no further mixing or agitation of the tank-mix is required.
Another way to overcome the solubility issues is to create a wettable powder. A wettable powder formulation is a dry, finely ground formulation. In this type of formulation, the active ingredient is combined with a finely ground dry carrier, usually a mineral clay, along with other ingredients that enhance the ability of the powder to be suspended in water. Upon mixing the wettable powder with water, a suspension is formed, which is then applied by a spray technique. Often the spray liquid must be continuously mixed to prevent settling of insoluble compositions.
However, wettable powders and soluble powder formulations tend to produce dust upon handling, such as when pouring, transferring or measuring them. This dust may pose health hazards. Further, powder formulations tend to wet poorly and also solubilize slowly upon addition to water. Powder formulations thus take longer to wet, disperse and solubilize in a tank-mix. Formation of lumps or partially solubilized spray solutions will lead to uneven distribution of the plant growth regulator in the tank-mix with the potential for reduced field performance. Sometimes, foam in the spray tank caused by spray tank adjuvants can also affect wetting and solubility of wettable and soluble powders. Wettable powder formulations will also leave undesirable insoluble residues both in the tank and on the sprayed foliage and fruit.
Another type of agricultural formulation is a tablet. Tablet formulations are pre-measured dosage delivery systems. They are useful in small areas, or for ornamental purposes. Tablet formulations may be effervescent, which dissolve in water over a period of two to ten minutes depending upon the type and size of the tablet. However, tablets generally deliver only between 0.1 to 1 gram of active ingredient per tablet. They are not ideal for large-scale field operations. Moreover, effervescent tablets are highly susceptible to humidity and may be slow to dissolve and are expensive.
Yet another type of agricultural formulation is a water-dispersible granule. Water-dispersible granules are also known as wettable granules or dry flowables. This type of formulation is similar to a wettable powder, except that the active ingredient is formulated as a dispersible granule. To prepare the water-dispersible granules for spray application, they are dispersed in water and form a suspension upon agitation. Many different water-dispersible granular formulations are known for agricultural chemicals. For example, EP 0 252 897 and U.S. Pat. No. 4,936,901 disclose encapsulated plant growth regulators in water dispersible granular formulations; and U.S. Pat. No. 5,622,658 discloses an extrudable composition for preparing water-dispersible granules.
Water-dispersible granules usually have no greater than eight percent moisture content, and form suspensions when added to aqueous solutions. The resulting suspension must be agitated for a period of time in order to fully disperse it. Agitation or by-pass recirculation of the tank-mix must also be maintained during application. The quality of water-dispersible granules is highly process- and active-ingredient-dependent; and can result in low yield recoveries, poor attrition resistance leading to dust potential, high manufacturing cost and poor dispersion. Generally, sprays of dissolved water-dispersible granular formulations leave undesirable insoluble residues on the treated foliage and fruit.
For GA3, GA4, and GA4/7 formulations to be efficacious, the active ingredient must solubilize in tank-mixes prior to application. Otherwise, product efficacy will be severely affected. When water-dispersible granules are used, the grower often may not realize if he has achieved complete solubility of the active ingredient in the spray solutions. In addition, water-dispersible granules can harden over time and thus result in poor dispersibility and solubility of the active ingredient. Dust and caking may be problems with certain water-dispersible granules and powder formulations.
Therefore, there is a need for environmentally safe, non-phytotoxic, efficacious, high strength gibberellin solution formulations. The improved formulations should overcome the toxicity, handling, storage, transportation, and solubility issues encountered by prior art formulations.